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81.
Stuart M. Barlow Anthony P. Bimbo Eric L. Miller Snorri Thorisson D. E. Walters 《Journal of the American Oil Chemists' Society》1997,74(9):1077-1083
Twenty-two laboratories participated in a collaborative test to determine the iodine value (IV) of eight samples of fish oil
(four with IV<150, four with IV>150) with either carbon tetrachloride (AOCS Official Method Cd 1–25) or cyclohexane (AOCS
Recommended Practice Cd 1b-87) as solvent and either 1 or 2 h of reaction time. Laboratories received coded duplicate samples
(hidden duplicates) and carried out duplicate determinations on each oil by each solvent-time combination (open duplicates).
Replacing carbon tetrachloride with cyclohexane resulted in a lower IV (P<0.001). The decrease averaged 1.6 IV units for low-IV oils and 3.8 IV units for high-IV oils; this difference in response
of 2.2 IV units between low- and high-IV oils was significant (P<0.001). Increasing the reaction time had a relatively small effect (0.34±0.18). There was no interaction of reaction time
with solvent or oil type. Cyclohexane caused emulsions, which made it difficult to titrate residual iodine and thus increased
the variability of the determination. The repeatability standard deviations (s
r
), based on hidden duplicates, for 1-h reaction time with carbon tetrachloride and cyclohexane were 2.17 and 3.35, respectively.
The corresponding reproducibility standard deviations were 2.73 and 4.53. 相似文献
82.
A relatively simple instrumentation system is described which samples and records the body temperatures from up to twelve experimental animals over long periods of time. Body temperatures are sensed by temperature-sensitive FM transmitters implanted in the peritoneal cavities. The emitted signals are received by antennas, amplified, and sequentially gated into a frequency counter for counting; the resulting digital numbers are recorded in binarycoded decimal (BCD) format on punched paper tape. Samples can be spaced at intervals of from 1 to 60 minutes, and sampling can be continued over long periods of many months. This system eliminates the need for analog-to-digital conversion and allows rapid and direct transmission of the raw data to the digital computer for processing and analysis. 相似文献
83.
Saleh Al-Sayari Albert F. Carley Stuart H. Taylor Graham J. Hutchings 《Topics in Catalysis》2007,44(1-2):123-128
The preparation of Au/ZnO and Au/Fe2O3 catalysts using two coprecipitation methods is investigated to determine the important factors that control the synthesis
of high activity catalysts for the oxidation of carbon monoxide at ambient temperature. In particular, the factors involved
in the preparation of catalysts that are active without the need for a calcination step are evaluated. The two preparation
methods differ in the manner in which the pH is controlled during the precipitation, either constant pH throughout or variable
pH in which the pH is raised from an initial low value to a defined end point. Non-calcined Au/ZnO catalysts prepared using
both methods are very sensitive to pH and ageing time, and catalysts prepared at a maximum pH = 5 with a short ageing time
(ca. 0–3 h) exhibit high activity. Catalysts prepared at higher pH give lower activity. However, all catalysts require a short
operation period during which the oxidation activity increases. In contrast, the calcined catalysts are not particularly sensitive
to the preparation conditions. Non-calcined Au/Fe2O3 catalysts exhibit high activity when prepared at pH ≥ 5. Calcined Au/Fe2O3 prepared using the controlled pH method retain high activity, whereas calcined catalysts prepared using the variable pH method
are inactive. The study shows the immense sensitivity of the catalyst performance to the preparation methods. It is therefore
not surprising that marked differences in the performance of supported Au catalysts for CO oxidation that are apparent in
the extensive literature on this subject, particularly the effect of calcination, can be expected if the preparation parameters
are not carefully controlled and reported. 相似文献
84.
David A. Woodford Donald R. VanSteele Mohammed J. Hyder 《Journal of the American Ceramic Society》1991,74(12):3142-3144
The development of a tensile testing methodology for ceramics which enables a stress vs strain-rate response to be measured at high temperature is described. The test involves a carefully controled stress relaxation test at constant total strain using an experimental procedure and phenomenological analysis previously developed for metallic materials. It is demonstrated here with preliminary tests on alumina at 1050° and 1150°C. This offers, with further development, the possibility of establishing design stresses associated with low strain-rate behavior for structural applications. The results demonstrate that data covering four decades of strain rate may be generated in tests lasting a few hours. The inelastic strain consists of substantial anelastic recoverable strain in addition to a permanent creep strain. 相似文献
85.
Douglas A. Weirauch Jr. Donald P. Ziegler 《Journal of the American Ceramic Society》1996,79(4):920-926
Numerical analysis is used in this study to derive surface tension from the shape of a liquid silicate sessile drop. The speed afforded by the drop shape analysis package facilitates analysis of experimentally derived drop profiles. Drop symmetry, contact angles, and local shape variations can be readily determined, thereby permitting the detection of experimental errors. The experimental and analytical technique was first validated by determining the surface tension of high-purity gallium and aluminum under carefully controlled furnace atmospheres. Results for a calcium aluminosilicate melt are compared to pendant drop and maximum-bubble pressure measurements reported in the literature. The use of an internal scaling factor and the effect of substrate interactions are discussed. 相似文献
86.
Maria Luz Fernandez A. Karin Conde Laura R. Ruiz Carlos Montano John Ebner Donald J. McNamara 《Lipids》1995,30(7):619-626
To test the effects of exchanging dietary complex and simple carbohydrate for fat calories on lipoprotein metabolism, guinea
pigs were fed two different fat/carbohydrate ratios: 2.5∶58% (w/w) or 25∶29% (w/w) with either sucrose or starch as the carbohydrate
source. Animals fed high-fat had higher plasma low-density lipoprotein (LDL) and hepatic cholesterol concentrations than animals
fed low-fat diets (P<0.01). The cholesteryl ester content per particle was higher, and the number of triacylglycerol (TAG) molecules was lower
in very low density lipoprotein (VLDL) and LDL from animals fed high-fat diets. Intake of high-fat/sucrose resulted in higher
plasma LDL concentrations than intake of high-fat/starch, and animals fed low-fat/starch had the highest plasma TAG concentrations
associated with VLDL particles containing more TAG molecules, as well as a TAG-enriched LDL. The activity of plasma lecithin
cholesteryl:acyl transferase (LCAT) was highest in animals fed high-fat/sucrose, and heart lipoprotein lipase (LPL) activity
was higher in animals fed high-fat diets. Hepatic apoprotein B/E (apo B/E) receptor number (Bmax) was increased 21% with low-fat diets (P<0.01). These results suggest that the hypercholesterolemia induced by high-fat and by sucrose intake are associated with
a higher plasma LCAT activity which results in a cholesteryl ester-enriched VLDL which, by the action of LPL, might be more
readily converted to LDL through the delipidation cascade leading to downregulation of hepatic apo B/E receptors. The hypertriglyceridemia
associated with low-fat intake may result from increased production of VLDL TAG, which would explain the increased TAG content
and the higher TAG/CE ratio of VLDL from animals fed the low-fat/starch diet. 相似文献
87.
The attrition mill is a device for mechanically reducing solid particle size by intense agitation of a slurry of material being milled and coarse milling media. For example, in 10 hours of milling, specific surfaces of 40 and 25 m2/g were obtained for alumina and barite, corresponding to 38 and 56 nm equivalent spherical diameter, respectively. Size reduction rates for relatively coarse particles were first-order and increased linearly with power input to the mill. Optimum milling medium concentration corresponded to medium particles moving a distance of approximately 0.7 of their diameter before collision with another such particle. Power characteristics of the attrition mill were essentially the same as those of a radial flow turbine mixer. Laminar flow became disrupted at NRe ≈ 200, while turbulent flow was established at NRe > 8000. Slurries of fine powders exhibited the same linear power-average density dependence as single-phase liquids. However, a different dependence was observed with large particles. 相似文献
88.
89.
Experimental measurements were made of the pH, density, bulk viscosity and electrical conductivity of aqueous solutions of sodium lauryl sulphate for a wide range of concentrations at 25°C. Also, the time-dependent interfacial tension data of this system with mutually saturated benzene phases are reported. Comparison of these data with literature values shows fair agreement in the majority of the cases and further reveals the lack of data in the earlier investigations below the critical micelle concentration of sodium lauryl sulphate in water. A detailed compilation of the data, reported in the literature since 1937, of the pH, density, bulk viscosity, electrical conductivity, surface tension, interfacial tension with benzene, surface excess concentration, surface shear viscosity, diffusivity and critical micelle concentration of the sodium lauryl sulphate system is given. The importance of this anionic surfactant system together with the various factors which influence the physical properties is examined. 相似文献
90.
Donald J. Gray 《Chemical Engineering Communications》1987,61(1):151-158
The effect of impeller off bottom clearance on the power input requirement for off bottom solid suspension was examined for 45° pitched blade impellers in flat and round bottom fully baffled agitated vessels. Results showed a similar dependence as obtained for radial flow impellers when similar flow patterns were observed. The dependence appears to be independent of the impeller diameter to tank diameter ratio and vessel shape. 相似文献